Is IPv6 prefix delegation configurable?

[spike <spike fedoraproject org>]

Hi,

I've finally figured out how to do prefix delegation thanks to the comments in this issue: 
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/375

It seems that NetworkManager always uses the first /64 from the delegated prefix and assigns ::1 as the 
interface address. Is that configurable, e.g. could I tell NetworkManager to use a /56 from the delegated 
prefix or the the n'th /64 network? How about the interface address?

Can't seem to find any documentation on this but it's very well possible that I just didn't look thoroughly 
enough. Any pointers are appreciated.

Cheers!